The overall objective of this research protocol is to assess and evaluate the hemodynamic deterinants of the intensity of myocardial relaxation in the intact heart and to determine the influence of altered relaxation on left ventricular (LV) diastolic compliance. Experiments will be performed in the anesthetized dog, and attempts will be made to extrapolate the expermental findings to studies in man. In the animal studies, LV relaxation will be studied by measuring the time constant (T) of isovolumic exponential pressure decline; ultrasonic crystals (transit time) will be utilized to measure changes in myocardial segment length or LV chamber dimension. The determinants of T will be examined during acute alterations in LV preload, afterload, and contractility, and during several other interventions which will be designed to influence relaxation. LV diastolic compliance will be assessed through simultaneous measurements of LV pressure and dimension, and the influence of prolonged myocardial relaxation on diastolic compliance will be determined. Finally, attempts will be made to develop a load-independent index of relaxation. The second aim of this research plan is to define the values for T in humans with and without LV disease (cardiac catheterization) and to develop noninvasive (echocardiography) methods to evaluate LV relaxation. These proposed studies will provide new information regarding the process of LV relaxation, especially the influence of relaxation on LV diastolic compliance and the relation of relaxation to systolic contraction, both in the experimental animal and in patients with and without heart disease.